There are numerous other stronger studies over decades who have shown no such effect with viruses of this type.
In the July 14, 2020 “JAMA” online edition, this article was published:
“Universal Masking to Prevent SARS-CoV-2 Transmission—The Time Is Now”:
https://jamanetwork.com/journals/jama/fullarticle/2768532
These words are at the beginning of the article:
“prior to implementation of universal masking in late March 2020, new infections among HCWs with direct or indirect patient contact were increasing exponentially, from 0% to 21.3% (a mean increase of 1.16% per day). However, after the universal masking policy was in place, the proportion of symptomatic HCWs with positive test results steadily declined, from 14.7% to 11.5% (a mean decrease of 0.49% per day). Although not a randomized clinical trial, this study provides critically important data to emphasize that masking helps prevent transmission of SARS-CoV-2.”